The invention relates to a method for controlling a motor using pulse width modulation (PWM).
In vehicles, electric motors which are controlled using pulse width modulation are used for different purposes. Examples include fan motors and also electrical adjustment systems. In this case, an electric motor has an associated controller which generates a sequence of square-wave pulses of which the width is modulated. In this way, the energy which is supplied to the electric motor is modulated, as a result of which the speed can be controlled. Conventional controllers are operated at a constant PWM frequency which can be, for example, 18 kHz or 20 kHz.
It is known that driving electric motors by pulse width modulation causes interference which is expressed as acoustic interfering noise, for example, during radio reception. Interference can occur as harmonics of the PWM frequency and is audible particularly when the harmonic has a similar frequency to a set radio transmitter.
WO 97/05716 A1 proposes using filters for reducing the radio interference in order to avoid interference owing to a motor which is controlled using pulse width modulation. Capacitors are used as filters.
The use of coils which are arranged in the controllers, in addition to capacitors, is also known. However, EMC measures of this kind are costly and require a great deal of installation space on the printed circuit boards but are sometimes not sufficiently effective.